1. Field of the Invention
The present invention relates to a composite electrode active material and a supercapacitor, and more particularly, an electrode active material having M1-xRuxO3 (M=Sr, Ba, Mg) and a supercapacitor using the same.
2. Background of the Invention
Recently, environmental pollution and an exhaustion of energy resources are leading to active researches on development of environment-friendly alternative energy resources. In spite of development of batteries or fuel cells having high energy density, there are limitations on applying to an application field requiring high power density. A supercapacitor, which has been known to have superior power density characteristics to lithium secondary battery, attracts attention as a device, which can not only satisfy the power density required for hybrid electric vehicles (HEVs) or satellite communications, but also take the lead in reducing the size of an energy system by distributing energy of a battery or fuel cell.
Among various types of supercapacitors, pseudocapacitors having an energy storage mechanism achieved by virtue of ion absorption or oxidation-reduction reaction on a surface of a material satisfy requirements of high power and high energy density, as compared to an electric double-layer capacitor using carbon materials. So, studies on the type of capacitor are actively undergoing.
Among the pseudocapacitive materials, many studies on the use of ruthenium oxide (RuO2) having superior specific capacitance as an electrode have been done, but the high price of ruthenium oxide nanoparticles makes it difficult to apply the same to a mass production and a low-priced process. The ruthenium oxide exhibits very different properties in an amorphous structure and in a crystalline structure. The crystalline ruthenium oxide is known for its high electrical conductivity (specific resistance: 35 μΩ·cm), whereas the amorphous ruthenium oxide is known for its superior hydrogen ion (proton, H+) conductivity. Especially, the hydrated ruthenium oxide obtained through a low-temperature fabrication process has a high specific capacitance value due to the high ion conductive properties. However, the hydrated ruthenium oxide has a limit to be applied to high-speed supercapacitors due to its relatively low electrical conductivities as compared to the crystalline ruthenium oxide having high electrical conductivities.
Accordingly, a new composition material is needed which can lower the burden of high material cost of ruthenium oxide and simultaneously maintain high electrical conductivities and increase ion conductivities, with reducing the content of ruthenium. Especially, the development of a composite composition having a high specific capacitance value is demanded. Also, the development of an electrode with a nanostructure having both crystalline and amorphous properties is important for fabricating a supercapacitor with a high power and a high energy density.